#define SQR(x) x*x. Unexpected Answer

Question

Why this macro gives output 144, instead of 121?

#include
#define SQR(x) x*x

int main()
{
    int p=10;
    std::cout<         


        

Answer 1

Because you are using undefined behaviour. When the macro is expanded, your code turns into this:

std::cout<<++p*++p;

using increment/decrement operators on the same variable multiple times in the same statement is undefined behaviour.